| To reveal the action mechanisms and laws that water resource protection forest preserves and improves water quality and to offer academic elements of managing and supervising protection forest, this paper studies the chemical property of precipitation through collecting rainwater from canopy, trunk, litter and soil layer in Pinus tabuleaeformis water resource protection forest in Miyun Reservoir watershed, which based on the investigation and the laboratory works. Furthermore, this paper studies the sendout-concents of chemical elements through canopy and trunk by using distribution models of rainfall, which explains the mechanism of depuration radically.The program mainly deals with water conservation forest ecosystem in 2005. Ten chemical elements was analyzed of the water samples collected from rainfalls, stem-flow, through-flow, litter water and soil-layer water, the chemical elements including the nitrogen, phosphorus, potassium, sodium, calcium, magnesium, iron, zinc, copper and manganese.(1) The total rainfall was 636.3mm in 2005 from April to October, and the rainfall in August was morn than other months, which was 33.99% of total rainfall. After September, it gradually got less and to the least in October, which was only 0.44% of total rainfall. In a word, the total rainfall was usual in 2005 with other years. The rainfall interception occupied 20% of total rainfall and the through-fall occupied 75%. But the stem-flow occupied less than 8%.(2) The total concentrations of chemical elements in precipitation was 10.817mg·L-1 . It greatly varied in the rainfall periods and got to the most in July .The sequence of the concentrations in the precipitation was Ca>N>K>Na>Mg>Fe>P>Zn>Cu>Mn.(3) The concentration of total chemical elements of through-fall, stem-flow, litter water and soil-layer water were 14.011 mg·L-1, 29.165 mg·L-1, 20.724 mg·L-1 and 51.704 mg·L-1. we can conclude that: the contents of chemical elements of through-fall, stem-flow, litter and soil layer water were various, but the total contents increased in comparison with that of the precipitation and particularly it upsized greatly through soil layer. It is similar to studies of other scholars in our country.the contents of chemical elements in through-fall and stem-flow of three groups of standard trees were various , but got increase along with the diameter at breast height(DBH). The reason is that the trees which have big DBH would have big canopy, so the rainfall can eluviate more chemical elements.Comparing the contents of chemical elements in through-fall, stem-flow, litter water and soil-layer water of different months, we can conclude that the concentration of most elements got to the most in July, whicn is due to the most rainfall.(4) The sum of sendout-contents of chemical elements in through-fall was 84360.6g·hm-2·a-1 in 2005, and the sum of input-contents of chemical elements in rainfall was 68828.05g·hm-2·a-1.The input-contents were less than the sendout-contents. The sequence of sendout-contents of chemical elements in through-fall was Ca>N>K>Mg>Na>Fe>P>Zn>Cu>Mn, which is the same with the result of comparing concentration..The sum of sendout-contents of chemical elements in stem-flow was 4512.26g·hm-2 through studying six times rainfall and the sum of input-contents of chemical elements in rainfall was 20723.00 ghm-2 .The input-contents were more than the sendout-contents, which is different from the result of comparing concentration...
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